Separation of metals from zinc-bearing ores or compounds.



E. A. ASHCROFT. SEPARATION O1? METALS PROM ZINC BEARING 03158 OR COMPOUNDS.

APPLICATION FILED APBJS, 1912.

Patented M31124, 19m

. M ,6 a g il l'luesses Y EDGAR ARTHUR ASHCROFT, 0F BALESTRAND, SOG-N, NORWAY.

SEPARATION OF METALS FROMZINC- BEARIN G- ORES OR COMPOUNDS.

Specification of Letters Patent.

Patented Mar. 24., 1914..

Application filed April 2'5, 1912 Serial No. 693,150,

To all whom it may concern:

Be it known that I, EDGAR ARTHUR ASH- onor'r, a subject of the King of England, residing at Balestrand, Sogn, Norway, have invented certain new and useful Improvements in Separation of Metals from Zinc- Bearing Oresor Compounds, of which the following is a specification.

The invention has special reference to the more economical treatment of zinc bearing sulfid ores or concentrates or residues or of solutions of chlorid, sulfate or other salts of zinc such as may be produced from such material by various known .ways. Also to improvements in the electrolytic separation of zinc from the fused salts resulting from such operations and to the production of various by-products.

The invention is especially character zed by the employment of ammonia toprempitate the metals present, for instance, 1n a chlorid solution, as hydrates, (which affords a ready means-of obtaining the zinc separated from other metals such as iron, aluminum, Calcium, manganese and the like) and after separation of the superfluous metals and salts heating the zinc hydrate with ammonium chlorid to form pure fused zinc chlorid and recover the ammonia; also by.

- further improvements relate to the method of electrolysis and apparatus therefor all as more fully set out hereafter.

This invention may very conveniently be worked in conjunction with the three processes described in my U. S. Patents Nos. 1011897, 1011898 and 1011899 granted to me wherein are described improved processes for treatment of various well-known zinc bearing ores each process being more suitable for a certain class of material.

The present invention has a wider scope of utility and may be applied to every kind of zinc bearing ores, residues, concentrates or solutions from which it is desired to obtain zinc or lead in metallic form with simultaneous recovery of by-products metallic or otherwise.

In operating my improved process I proceed as follows 1 Step 1.

Whatever the nature of the raw material Worked upon such of the zinc as is not readily obtainable as pure fused anhydrous chlorid by purification and decantation in the fused state (without the treatment herein described) is preferably first brought into crude solution in the form of chlorid of zinc. For instance Eaample .--A calamin slime, roasted ore or zlnky residue is dissolved by preference in hydrochloric acid and crude solutions of any desired strength may be readily thus obtained and the insolubles rejected.

Emamp le 2.A zinc sulfid concentrate or ore carrying Zn 40%, Pb 10%, Ag. 10 ozs. per ton S 25%, Fe 10%, Mn 2%, gangue 5%, may be treated preferablyfirst for elimination of lead and silver by process described in my U. S. Patent No. 1011897, and then by chlorin smelting with or without the process in the second converter for elimination of iron and manganese all as described in my U. S. Patent No. 1011899, and finally the impure melt consisting of zinc chlorid and various other chlorids, such as alumina and calcium (with ironand manganesewhen the second converter process has not been applied and small percentages of lead chlorid when the deleading process has been omitted or incompletely applied) is dissolved in water and the insolubles rejected. In most cases when a material of constant or nearly constant composition is being treated this solution will be treated cyclically as hereafter described and only the wash waters derived from washing the filtered 0H insolubles and lay-products need be added to make up the bulk of solution lost by partial evaporation in the final operation described below. The solution will be employed near to its boiling point at all parts of the cycle and its temperature will be maintained by the continual supplies of rejected after the first solution. ng with this class of ores it is very convenlent and economical to employ the sulfur gases escaping from the converters directly I for the production of a by-product of ammonium sulfate or sulfite or mixtures of these salts for which extensive uses are found in agriculture. For this purpose it is only necessary'to admit air or oxygen to burn the sulfur to SO which may then be combined with ammonia gas and water (preferably produced by the well-known reactions of calcium cyanamid or dicyandiamid with water etc), either with or without Previous oxidization of the sulfur to liquid H 80 The method I prefer for this purpose is to admit .abundant air to the gases escaping from the top of the converter and after coolingthe resulting gases to about 200 C. to admit ammonia gas and a small quantity of water vapor and after reaction again cool, which resultsin the direct and very economical production of a pure White salt mainly consisting of sulfate of ammonium in a high state of purity and very convenient physical condition. This salt has a high percentage of NH (25% to 30%) and is a most valuable agricultural dressing in great demand.

Step 2.

Having obtained a crude solution of zinc chlorid containing for example Zn(ll 136 grams per liter and NH Cl 265 grams per liter with iron, manganese and other metal chlorids in proportion to the zinc brought into solution at each cycle of operations, any known purifying process may be employed to eliminate undesirable elements from the neutral solution but I prefer to proceed as follows :Ammonia gas is passed into the zinc bearing solution (or ammonia solution in Water added thereto) until all the metals are precipitated as hydrates with corresponding formation of NH Cl (type reaction MCl +2NH +2H O=M (OH) 2NH Cl). Excess of ammonia is then added until the hydrates soluble in ammoniacal solution, in this case mainly zinc (and lead if present) are dissolved. In the presenceof ammonium chlorid some manganese will also be dissolved in the ammoniacal solution'and may be readily precipitated therefrom (after filtering off the iron hydrates) by a slow stream of chlorin. In this way the ferric and manganic hydrates 7are obtained separately and in a high state of purity which gives them a special value as by-products. For instance the ferric hydrate so obtained produces a high quality of Vermilion paint after roasting.

Step 3.

The Whole of the zinc may be readily obtained from these purified ammoniacal'solutions in the form of zinc hydrate In Work-' (Zn(OH) by merely driving off the excess of ammonia by heat or by neutralizing it with a further proportion of zinc chlorid in purified neutral solution or by an acid with formation of ammonium salts (preferably chlorid). typical of this part of the process.

On heating alone.

(1) Zn(OH) NH4(OH) Zn(OH) -l-H O+NH Insoluble zine hydrate. Gas. Precipitation by neutral zine e/zloriol solution.

(2) 2Zn(OH) NH (OH)+ZnCl 3Zn(OH) +2NI-LCL Insoluble hydrate.

Precipitation by an acid.

Soluble zine salt.

Soluble zine salt.

Step 4.

Finally the ammonium chlorid so formed (in molecular proportions or excess) is added to the precipitated zinc hydrate either as a concentrated solution (in which the presence of some zinc chlorid is .of course in no Way detrimental so long as the total ainmoniuni chlorid is in excess of that required for the reaction given below) or as crystallized salt or in any .other form and the mixture is slowly distilled in suitable vessels (for instance large enameled iron or glass retorts) at a low temperature first to drive oil water and then rising to about 300 C. when all the zinc present will be converted to fused zinc chlorid and the ammonia will be driven off and may be recovered in any convenient way for use again. This reaction is as follows It is not necessary to previously dry the zinc hydrate or the ammonium chlorid. Any water remaining is driven off with the ammonia as well as the water produced by the reaction and at the end of the reaction the temperature is raised to about 500 C., which will drive off all the excess of NILCI which happens to be present. While still at this temperature it is preferable to pass in a slow stream of chlorin for some hours The following reactions are a which will result in a pure, Water-free, and

neutral zinc chlorid very suitable for electrolysis by the following improved system.

lution thus allowing a minimum of apparatus to be employed and minimum handling of materials. The resulting zinc chlorid is a product of high purity practically free from ammonium'chlorid and fio-m water and is eminently suitable for electrolysis in the fused state. Lead chlorid if present in the solutions will'be found also in the final melt but. in no way interferes with the re-- actions or with the final treatment.

Step 5.

Electrolytic treatment of fused chlorid.- To insure the most economical electrolytic arrangement it is preferable to heat the metal cathode from below while only a short gap and a thin layer of fused chlorid is maintained over the surface thereof. A current density of about 3 amperes per square centimeter of exposed anode surface may be used and 2.5 volts per vat will suffice under these conditions. The temperature is best kept at 450C. In' order to heat the vat from below without destroyingthe metal vessels, I prefer to employ a-bath'of molten lead as cathode which may be drawn offand renewed frequently or circulated continuously while the zinc alloy accumulates there in. The zinc ou standing floats to the top and the lead sinks to the bottom audit is well known that a separation of lead from zinc or zinc from lead sufiicient for nearly all commercial purposes can be readily made in a simple furnace in this manner. arrangement has the further advantage that either zinc chlorid or lead chlorid or both atonce can be decomposed in the same apparatus so that it becomes quite unnecessary to direct specialattention to the-complete separation of lead in the earlier stages of the treatment of an ore.. It will be sufiicient in fact to extract the silver content of a leady zinc concentrate and perhaps twothirds of the lead by the deleading process U. S Patent .No. 1011897. The-remainder of the lead will pass through the converter and the solutions and appear again in the final product of the electrolytic vats to which This also the lead chlorid recovered from the deleading process may conveniently be added for recovery of lead and chlorin.

The form of electrolytic vat )referred for carrying this invention into e ect is shown in the accompanying drawingin which- Figure 1 is a sectional elevation of the vet, and Fig. 2 is an end elevation partly insection.

The vat (say for the employment of 5,000 to 10,000. amperes per unit) is constructed in the form of a long trough A furnished with a number of parallel graphite anodes B of convenient dimensions say 10 of 300 square centimeters exposed surface area (say cylinders of 20 centimeters diameter). Around each of these anodes is placed an inverted bell C, constructed of any suitable material, such as hard glass or enameled iron, in order to recoverthe chlorin undiluted with air; the rim of the bell just dippinginto the electrolyte D and leaving amarginal space of fused electrolyte open to'the air for feeding the vat with fresh chlorids or for cleaning or other manipulation. A convenient pipe E conducts chlorin from each bell to the stationary chlorin -mains F leading to. the pumps and converters." The bells are made capable'of readyremoval and replacement 1n case of breakage or for the purpose of removing the deposits of zinc chlorid which are found thereonfrom time to time (having been carried off from the hot electrolyte with the ..escaping gases and condensed on thenearest cold surface).

G is the cathode of molten lead. Preferably the vat A- is lined on all sides with a fireclay lining H. The lining extends to the bottom of the vat but does not extend thereover. The working of this apparatus is very. perfect, a current efiiciency of 85% may be readily obtained and quite pure chlorin gases collected. The latter is of course used in the'convertersior may be applied to any other purpose. The production of zinc is 2.5 tons, of lead 10.0, tons per electric horse power which is greater than by, any hitherto known process of either electric smelting or electrolysis.

. The four examples given above of course only describe leading or typical lines of procedure which may be varied in a great variety of ways without departing from the spirit of this invention.

The above process as a whole and in its various parts presents'great economical advantages among which may be briefly stated the following :-1. Complete cyclic working is obtained without the employment of a secondary electrolytic device or a secondary converter arrangement. I 2. Several valuable by-products are directly produced in marketable form. 3. Verylow total consumption of electric energy. 4. Complete recon eries of metals. 5. Complete recovery of chlorin. 6. Small and inexpensive appa ratus. 7; Total avoidance of the expensive item of boiling down solutions ofizinc chlorid to the fused state. 8. Small Wear and tear of apparatus, all the solutions, etc.,

being basic except for the final fusion electrolysis which is neutral and the converter for which special imperishable material may be readily employed.

' What I claim as m invention and desire to secure by Letters atent is V 1. The herein described process for obtaining metals from solutions of various metallic salts roduced from zinc bearing sulfid ores which consists in precipitating the metals other than zinc and manganese from such solutions by "the addition of an excess of ammonia, separating the precip'b' tated hydrates from the solution, precipi-r tating the manganese and separating it from the remaining solution, precipitating the zinc hydrate from the purified solution and re-acting it with ammonium chlorid ata temperature sufiicient to convert the zinc K into thefused chlorid and to drive oft the ammonia.

2. The herein described process for obt-aining metals from solutions of various metallic salts produced from zinc-bearing sulfid ores which consists in precipitating the metals as hydrates with ammonia, adding excess of ammonia to dissolve the zinc, lead, manganese and other hydrates present soluble in excess, separating the precipitat-ed hydrate from the solution, precipitating the manganese by a slow stream of chlorin and separating it from the remaining solution, precipitating the zinc hydrate by adding to the solution a further quantity of purified zinc chlorid and reacting ble in excess, separating the precipitated hydrates from the solution, precipitating the manganese by a slow stream of chlorin and separating it from the remaining solution, precipitating the zinc hydrate by adding to the solution. a further quantity of purified zinc chlorid, mixing with the precipitated zinc hydrate the ammonium chlorid separated from the solution by crystallization, thereafter distilling the mixture 'firstly at a low temperature to drive off the Water, secondly at about 300 C. to convert the zinc to fused Zinc chlorid, and to drive off the ammonia, recovering the ammonia,

and thirdly raising the temperature to about 500 C. to drive 0 the excess of ammonium chlorid.

In testimony whereof I have signed my name to this specification in the presence of 79 two subscribing Witnesses.

EDGAR ARTHUR ASHCROFT.

Witnesses PAUL ARRAS, Cnlinn SIMON. 

